Semiconductor devices such as diodes applied to a high withstand voltage power module or IGBT are provided with a termination region around an active region to improve a withstand voltage. Here, the active region refers to a region through which a main current flows when a semiconductor device is ON. The termination region is a region in which no main current flows in an ON state and which extends a depletion layer in a lateral direction of the device to maintain the withstand voltage in an OFF state (when a reverse bias is applied).
In conventional semiconductor devices, carrier concentration increases on a boundary between a termination region and an active region during a recovery operation, electric field strength on an anode side thereby increases and exceeds critical electric field strength, which promotes impact ionization. When a current density in this part increases, local temperatures thereby increase and exceed a critical temperature (800 K or higher) to lead to thermal destruction (e.g., see Non-Patent Literature 1). As a countermeasure for this, there is a proposal of providing a ballast resistor at an end of an anode layer of the active region (e.g., see Non-Patent Literature 2).